Centre for Environment, Fisheries & Aquaculture Science (Cefas), Aquatic Health and Hygiene Division, Food Safety Group, Weymouth Laboratory, Weymouth, Dorset DT4 8UB, UK.
J Water Health. 2011 Jun;9(2):368-81. doi: 10.2166/wh.2011.136.
Rainfall and river flows are environmental variables influencing the microbial status of bivalve mollusc harvesting areas. This study investigated spatial and temporal relationships between rainfall, river flows and concentrations of Escherichia coli in mussels (Mytilus spp.) and Pacific oysters (C. gigas) from three harvesting areas in the Dart Estuary over the period 1996-2009. Mussels growing on the riverbed were found to be more contaminated than oysters growing in the water column. A step change in the levels of the microbial indicator was identified in both species from all harvesting areas. The highest levels of E. coli were detected when total rainfall exceeded 2 mm and water levels in the main tributaries exceeded the mean flow. The magnitude of response in levels of E. coli to these hydrological events varied between species and monitoring points, but was consistently higher between the 3rd and 4th days after the rainfall event. This lag time is assumed to result from catchment topography and geology determining peak levels of runoff at the headwaters 12-24 h after rainfall events. It is considered that future risk management measures may include sampling targeting hydrograph events.
降雨和河川流量是影响双壳贝类捕捞区微生物状况的环境变量。本研究调查了 1996-2009 年间 Dart 河口三个捕捞区的降雨、河川流量与贻贝（Mytilus spp.）和太平洋牡蛎（C. gigas）中大肠杆菌浓度之间的时空关系。研究发现，生长在河床的贻贝比生长在水层中的牡蛎污染更为严重。所有捕捞区的两种贝类都出现了微生物指标水平的阶跃变化。在总降雨量超过 2 毫米且主要支流水位超过平均流量时，两种贝类的大肠杆菌水平都达到了最高值。大肠杆菌水平对这些水文事件的响应幅度因物种和监测点而异，但在降雨事件发生后的第 3 至 4 天始终更高。这种滞后时间被认为是由集水区的地形和地质决定的，在降雨事件后 12-24 小时，集水区的上游达到径流水位的峰值。未来的风险管理措施可能包括针对水文事件的采样。
